Observation devices suitable for the magnified imaging and optical evaluation of samples are actually known in the form of light microscopes. With light microscopes, a resolving power is achieved that is about 1000 times that of the human eye. In addition to this relatively high resolution, it is necessary in many light-microscopical examinations to carry out a detailed analysis of the chemical element composition of particular regions of the sample, identified by means of the light microscope, e.g., in order to characterize undesirable inclusions in metallurgical samples.
In the prior art, such detailed analyses are, as a rule, carried out with a scanning electron microscope, which, in imaging the sample surface by means of secondary electrons, yields an even substantially higher resolution of better than 1 nanometer (nm). In chemical analyses by X-ray spectroscopy with the scanning electron microscope, however, the best possible resolution is within a range of 0.5 to 2 micrometers (μm) and is determined by the volume of interaction of the electron beam with the sample.
For examining one and the same sample, thus, it is necessary to change from one instrument to another, which involves a considerable interruption of the work flow, as the examination of the sample in the scanning electron microscope takes place in a vacuum, for which reason the sample taken from the light microscope first has to be brought into a vacuum through a lock, after which the sample region of interest has be found again in the scanning electron microscope and positioned.
Added to this may be waiting time for the availability of a scanning electron microscope, and furthermore there is the risk of the sample getting damaged during transfer between the instruments. Moreover, a scanning electron microscope is a relatively expensive investment, the technical capabilities of which are required to a limited extent only, if at all, for solving the problem mentioned above, i.e. the analysis of a chemical element composition after light-microscopical examination.
U.S. Pat. No. 6,452,177, for example, describes an electron-beam-based material analysis system which is suitable especially for examinations under atmospheric pressure. This system has the drawback that it is unfit for microscopical observation of the sample. Moreover, the sample region in which the material is to characterized is dot-shaped and relatively large, i.e. >100 μm; there is no shielding against the X-ray radiation, and the time required for a measurement is relatively long. Another drawback is that the electrons escape from the vacuum of the electron source to the surrounding atmosphere through an electron-transparent membrane. This leads to increased scattering, which is a disadvantage especially for examinations at high resolution. Furthermore, the electron scattering produces X-ray radiation, which is superimposed on the signal measured of the sample, thus degrading the quality of the measurement signal.